The present invention relates to a facsimile apparatus employing a serial printing device that reciprocates a serial printing head in a main-scanning direction while shifting a recording sheet in a subscanning direction.
Conventionally, various facsimile apparatuses comprising a printer of a serial printing method have been introduced. In these facsimile apparatuses, if an ink-jet printing head is employed as the printing head, cleaning/recovery operation is performed at predetermined intervals in order to avoid poor ink-discharging by the printing head. However, the period between the cleaning/recovery operations is very long, e.g., once in several days.
Further, these apparatuses do not perform any preprinting function, such as preparation for printing operation, by moving the carriage that holds the printing head. Also, these apparatuses do not perform functions related to moving the carriage before printing.
On the other hand, in a case where the serial printer drives the carriage by a step motor, driving load is the greatest when starting to drive the carriage from a home position. This causes insufficiency of torque at the step motor. Especially, if the time the carriage is held is prolonged, the driving becomes impossible.
One of reasons for the driving impossibility is non-printing status for a long period. This shifts the position of a rotor with respect to a stator within the step motor from an excited phase of an exciting signal for the step motor. Normally, the latest excited phase of the stopped step motor is maintained until the next exciting signal is applied. When the step motor is stopped for many hours, the exciting signal is turned off in consideration of safety. Basically, if the exciting signal is turned off for hours, the motor phase may be shifted for some reason, and in this case, the shifted phase does not correspond to the start point of the next exciting signal. This results in synchronization error status where the step motor cannot operate in synchronization with the exciting signal.
Another reason for a driving impossibility from a mechanical standpoint is a slight deformation and/or burr at a guide shaft for conveyably guiding the carriage or at a contact portion between the carriage and the guide shaft. In this case, the carriage might be settled on the guide shaft at a position where greater torque is required for driving the carriage.
In a case where the printing head mounted on the carriage is an ink-jet head, a capping operation at a carriage stand-by position is necessary to prevent drying of ink. However, long unused status increases the carriage driving load and cap-removing load by drying of ink, fixing of ink, evaporation of ink, further, cap-removal operation.
Further, as the period during which the carriage is stationary at the home position without any printing operation becomes longer, the change of environment around the apparatus must be considered. For example, temperature and humidity may affect change amount of mechanical deformation for driving the carriage, ink-drying/evaporation amount, and drying of grease at an carriage moving portion, further, load-increasing amount caused by waterdrops. Especially, in a facsimile apparatus which is often used in an "operatorless" state, careful study addressing this problem due to the above-mentioned causes is necessary.
That is, for example, upon starting printing after a long idle period, the load increased by the above causes results in synchronization error between the step motor and the exciting signal, due to torque insufficiency, so that the printing point is shifted or even printing becomes impossible.
If an operator is near the facsimile apparatus, as in normal printing operation or copying operation, the operator can deal with the printing-impossible status or poor printing, by retrying printing, and the problem is at most a waste of paper. However, if the apparatus is used in mode where printing cannot be retried, e.g., facsimile automatic-reception mode in which an automatically-received image is printed, the reception cannot be retried. In this case, the above statuses are not negligible any longer.
In some conventional printers, an initial operation of the carriage is performed upon turning on the power, and if the carriage does not move to the home position, an error indication and instruction for removing the error are displayed.
However, in a case where a serial printing device is used as a printer of a facsimile apparatus, the power of the facsimile apparatus is always on (stand-by), and in many cases the apparatus starts operatorless printing. For this reason, the error display is not useful.
In a printer using serial printing method, the power is turned on at every time it is used, therefore slight shift of the carriage is adjusted at this power-on operation. However, as mentioned above, a facsimile apparatus is always on, therefore, the shift of the carriage cannot be adjusted, and the shift may increase until it can be ignored no longer.